Brief (transient) or prolonged restriction of blood flow to an organ or tissue results in ischemia, an insufficient supply of oxygenated blood to that organ or tissue. In a clinical sense, ischemia is typically caused by partial or complete obstruction of a blood vessel, such as by stroke, myocardial infarction, or surgery in which the blood supply to the organ is reduced or cut off. It occurs also when an organ or tissue subject to transplantation or grafting, respectively, becomes ischemic after removal from the body. Reperfusion is the process of restoring blood supply to an organ or tissue after an event that restricts or blocks blood flow, for example by removal or lysis of a thrombus. Reperfusion also occurs following organ transplantation when the circulation is re-established.
Transient ischemia produces reversible injury in many organs. However, re-establishment of the circulation is associated with pathological changes that exacerbate tissue damage, and is typically referred to as IRI. This type of injury significantly reduces the success of recovery from stroke, myocardial infarction, organ transplantation and other types of surgery.
IRI is a complex process and the underlying pathogenetic mechanisms are not fully understood. Several earlier experimental animal and clinical studies, however, provide insight on the subject. For example, myocardial infarctions in rabbit hearts (Farb et al. J. Am. Coll. Cardiol. 1993; 21: 1295) and human hearts (Nijmeier et al. Int. Immunopharmacol. 2001; 1: 403) provide a model of IRI: myocytes are viable before reperfusion then progress to irreversible injury during reperfusion. Apoptosis can contribute to myocardial cell death during reperfusion, demonstrated by the finding that caspase inhibition protects against lethal reperfusion injury (Mocanu et al., Br. J. Pharmacol. 2000; 130: 197). IRI is also lessened when leukocytes are depleted (references in Nijmeijer et al., 2001).
Phospholipids are asymmetrically distributed in the plasma membrane bilayer of normal cells. The acidic phospholipid phosphatidylserine (PS) is confined to the inner layer facing the cytoplasm (Devaux and Zachowski, Chem. Phys. Lipids 1994; 73: 107) and maintained in this orientation by an ATP-dependent phospholipid translocase. When ATP is depleted (for example, as a result of anoxia) some PS translocates to the outer layer and is accessible on the cell surface. This process has been assayed by flow cytometry using a fluorescently labeled protein that binds PS with high affinity, such as labeled annexin V (Bossy-Wetzel and Green, Methods Enzymol. 2000; 322: 15).
Even though many advances have been made in surgical technique, patient management, and immunosuppression, IRI remains an important clinical problem. IRI accounts for as much as 10% of early graft loss in the case of transplanted livers (Amersi et al., J. Clin. Invest. 1999; 104: 1631). In addition, preservation of livers longer than 12 hours is highly correlated with primary nonfunction after transplantation, as well as an increased incidence of both acute and chronic rejection (Fellstrom et al., Transplant Proc. 1998; 30: 4278).
In spite of extensive research, including that reviewed by Selzner et al. (Gastroenterology 2003; 125: 917), no method for decreasing IRI has become widely used in the treatment of stroke or myocardial infarction, or in organ transplantation or tissue grafting. It would be desirable to develop a therapeutic agent or procedure which attenuates or prevents IRI from stroke or myocardial infarction, following organ transplantation, and in other surgical procedures.
d'Amico et al. (FASEB J. 2000; 14: 1867) mention that annexin V did not inhibit RI in the rat heart whereas lipocortin I (annexin I) did.
Pelton et al. (J. Exp. Med. 1991; 174: 305) mention that a fragment of lipocortin I, injected into the cerebral ventricle of rats, decreased infarct size and cerebral edema after cerebral ischemia.
Against this background, the present disclosure is provided.